The present invention relates generally to data communications. More particularly, the present invention relates to a physical-layer device (PHY) having a serial interface and a magic packet circuit.
To conserve energy, many personal computers (PC) currently employ sleep modes that cause the PC to power off when not in use, for example at night or after a period of inactivity. However, these periods of inactivity are the ideal time for system administrators to perform software updates, hard drive backups, and the like.
Conventional magic packet technology permits a PC to be awoken from sleep mode remotely. According to this technology, the PC places an Ethernet controller in magic packet mode before the PC enters sleep mode. While in magic packet mode, the Ethernet controller, which includes a media access controller (MAC) and a PHY, remains awake while the PC sleeps, transmits no packets, and essentially ignores all incoming packets except magic packets, which are packets that include a particular predetermined pattern. Upon receiving a magic packet, the MAC wakes the PC (e.g., powers on the PC).
In systems where the Ethernet PHY and MAC are implemented or integrated on separate chips, the PHY and MAC are traditionally connected via a Gigabit Media Independent Interface (GMII), Reduced GMII (RGMII), or Serial GMII (SGMII) interface. The GMII and RGMII interfaces do not consume much power when there is no traffic, but require many more pins than the SGMII interface. The SGMII interface has the advantage of fewer pins, but consumes the same amount of power regardless of the operating speed of the PHY or the presence or absence of traffic.
Of course, it is desirable for the Ethernet controller to minimize power consumption while in magic packet mode. However, as mentioned above, an SGMII interface consumes the same amount of power despite the near absence of traffic in magic packet mode. In addition, the SGMII interface must remain active during magic packet mode in order to pass magic packets from the PHY to the MAC, where the magic packet circuit traditionally resides.